The present invention relates generally to the field of radiotelephone communication, and, more particularly, to performing a hand-over of a mobile terminal from one base station transceiver to another base station transceiver.
In radiotelephone communication systems that use code division multiple access (CDMA) technology, base station transceivers in the same geographical region typically share the same frequency or communication channel and use different pseudo-noise codes to avoid interfering with each other. Thus, as a mobile terminal travels throughout a geographic region, one or more “soft” hand-overs of the mobile terminal may occur from one base station transceiver to another. That is, the mobile terminal establishes a connection to a new base station transceiver candidate before terminating an existing connection with a current base station transceiver. In wideband CDMA systems, a mobile terminal may establish connections with up to three base station transceivers and select the one that provides the best service.
Unfortunately, if neighboring base station transceivers use two arbitrary frequencies or communication channels, then a mobile station may perform a “hard” hand-over between these neighboring base station transceivers. That is, the mobile terminal terminates its connection with a current base station transceiver before establishing a connection with a new base station transceiver candidate. This is sometimes called the “break before make” scenario. CDMA communication systems support channels around both the 800 MHz and 1900 MHz frequency bands. Thus, one base station transceiver may support channels in the 800 MHz band while a neighboring base station transceiver may support channels in the 1900 MHz band. A mobile terminal would, therefore, perform a hard hand-over between base station transceivers that support channels on these two different frequency bands. Note also, however, that even if neighboring base station transceivers use the same frequency band for communication, they may nevertheless use different frequencies or channels within the band, which again results in hard hand-overs of mobile terminals between the neighboring base station transceivers.
When a mobile terminal performs a hard hand-over between two base station transceivers, there is a risk that a call may be dropped as the connection with the current base station transceiver is terminated before a connection with the candidate base station transceiver is established.